1. Technical Field
The present inventive concept relates to a method of providing an operating voltage in a memory device and a memory controller, and more particularly to a method of controlling an operating voltage applied to an unselected word line in a memory device.
2. Discussion of the Related Art
After an erase/program operation is performed on a selected memory cell in a memory device, a trap charge occurs at an edge of a tunnel isolation layer in the memory transistor of the selected memory cell. The increase of the trap charge causes a decrease of memory cell current and an increase of the threshold voltage for turning the memory transistor of the selected memory cell ON. In other words, after the erase/program operation of the memory device, the threshold voltage of memory cells increases, expanding a threshold voltage distribution.
In a read operation, a read voltage VREAD is applied to a selected word line connected to a memory cell from which data will be read and a pass voltage VPASS is applied to unselected word lines (i.e., word lines other than the selected word line) to turn ON memory cells connected to the unselected word lines.
At this time, when the threshold voltage of a memory cell is lower than that of adjacent memory cells, an electric field applied to a tunnel isolation layer of the memory cell having the lower threshold voltage is reduced by the memory cells having the higher threshold voltage.
As a result, the threshold voltage distribution of the memory cell having the lower threshold voltage is more expanded.